Many persons with vision impairments use Braille to communicate and could benefit from improved, refreshable Braille displays. Electronic encoding and storage of data are now an established capability for Braille information, as is the distribution system for recorded media or electronic media. With the advent of personal computers and large CD-ROM database libraries containing millions of print characters, the blind need Braille displays that allow them complete access to the information displayed on a computer monitor or located on some data storage medium. Advanced Braille technology will offer the potential for dramatic improvements in telecommunications access for persons with sensory impairments, including access to databases, electronic mail systems, bulletin board systems and mail order systems. Miniature actuators for a low cost, high density, refreshable Braille display to enable persons with severe visual impairments to read out printed material recorded in computer memory or in another data storage medium are needed.
Numerous devices currently exist which convert stored data into a tactile representation. Braille characters may be displayed, a few at a time, on an array of "Braille cells." Each cell consists of a group of pins which may be individually raised from the surface of the device to form the particular Braille character desired. Each pin of each character must be independently actuated by a magnetic (see U.S. Pat. Nos. 4,194,190 and 4,571,190), piezoelectric (see U.S. Pat. Nos. 4,044,350; 4,283,178; 4,473,356; 4,758,165 and 4,879,698), pneumatic (see U.S. Pat. No. 3,659,354) or electromechanical (see U.S. Pat. Nos. 4,033,053; 4,898,536 and 4,191,945) device controlled by inputs from a data storage medium. Each of these devices requires a large number of actuation devices and a relatively large device for displaying the entire page. Such devices would be expensive and bulky.
U.S. Pat. No. 4,266,936 discloses a portable Braille display unit which presents an entire page of Braille characters by means of spring actuated pins controlled by bimetallic latches. An immediate tactile display is provided which may be read out and then refreshed to read out the next group of characters. Although this device is lighter in weight and smaller in size than the previous art, each cell involves a rather complex mechanism and an assembly of cells representing a line of text becomes quite expensive.
The Braille characters may also be embossed on paper by a special Braille printer (see U.S. Pat. Nos. 3,924,019 and 4,183,683.) The Braille printers are necessarily quite bulky and expensive and require the reader to wait for the material to be printed out before it can be read.
U.S. Pat. No. 4,687,444 discloses a position detecting mouse with a Braille display located on its upper surface. The mouse scans a single Braille cell through the text as the reader progresses but does not allow for the presentation of a complete page of text at one time.
Thus, key limitations for full-page, refreshable Braille displays are the cost and size of the mechanism. Solution of this problem must focus on the actuator method to temporarily produce raised dots, approximately 6000 or more per page. This new actuator method must allow sufficiently dense packing while having low power requirements and low cost. A page size of 11 by 11 inches, the page layout of the Perkins Brailler, is regarded by many as the most desirable page size. In addition, a display of 25 lines of 40 characters each has become the standard within the industry.
Recently, Joerg Fricke, in his U.S. Pat. No. 5,222,895 issued Jun. 29, 1993, disclosed an input/output device which employs an electrorheological fluid to drive tactile display elements. Electrorheological fluids experience a substantial increase in viscosity when subjected to a strong electrostatic field. Fricke's device has several advantages over the earlier art, including smaller size display elements and a reduced number of moving parts. These advantages result in a page-sized display produced at a lower cost than what was previously possible. The half-cylindrical electrode geometry disclosed in Fricke's device, however, will inhibit the use of printed circuit techniques in the manufacturing process. These techniques lend themselves much better to manufacturing flat surfaces. Use of the half-cylindrical electrode configuration to apply voltage across the electrorheological fluid also induces a voltage gradient across the electrorheological fluid rather than a desired uniform voltage, therefore requiring higher voltage supply to the electrodes which reduces the efficiency of the device. Also, the electrical drive circuitry disclosed in Fricke is required to control voltage to either two or four electrodes for each dot. With 6000 or more tactile dots required for a single page of Braille characters, the number of electrodes required to be driven for a single dot is an important cost consideration. In addition, Fricke's device requires multiple voltage supplies rather than a single voltage supply. Lastly, Fricke's device appears to require the flow system to be pressurized and unpressurized for each cycle of dot actuation. It would be advantageous to have a device which allows for the use of printed circuit techniques, avoids pressurizing and unpressurizing the fluid flow system, minimizes the number of electrodes required to be driven, and minimizes the high voltage requirement.